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Old 11-04-2002, 06:49 PM   #1
ron_c1
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Default what are ALL the functions of the OEM EGT sensor??

ok...i think this is a pretty good question... my EGT sensor just failed, rendering my car something thats looks nice in the driveway but nothing more over the weekend.... i know that the sensor is there basically to let the ECU know if the temp is getting close to a level that could melt the cat in the uppipe.... what else will this trigger? i noticed quite awhile ago that peak boost was down 1-2 psi, and thought it may have been a leak....no leaks were found though. ....could that have been a sign that the sensor was on its way out?? ....just a thought i had....because once i did the 2.2kohm resister....boost was back up to where it was a few months ago... so, is boost limited based on values read from that sensor??
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Old 11-04-2002, 08:37 PM   #2
nhluhr
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the stock EGT sensor ONLY is there to monitor the condition of the pre-turbo catalytic converter. It has no function for tuning the car's ignition or fueling.

However, if it detects that the third cat has overheated (and is in danger of crumbling and/or catching on fire), the ECU may very well put the car into "limp mode" which would essentially eliminate any good power and boost.

If you have eliminated the pre-turbo cat (with an aftermarket uppipe), then you have no reason to keep this sensor in place so doing the 2.2kohm resistor mod + 12x1.25mm bolt makes great sense. You'll never get an EGT-probe-related CEL from the resistor and the bolt in place of the probe will offer less flow restriction in the uppipe since the bolt won't actually protrude into the uppipe like the probe does.

cheers!

-Nick
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Old 11-04-2002, 08:41 PM   #3
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and to back up my statements, here's the page from the Factory Service Manual that tells what factors the ECU uses to adjust the air/fuel ratio:


Notice, in the correction factors, EGT is NOT listed.

Last edited by nhluhr; 11-04-2002 at 08:50 PM.
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Old 11-04-2002, 08:49 PM   #4
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and here is the page from the manual that talks about the EGT probe itself:

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Old 11-04-2002, 08:52 PM   #5
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Quote:
Originally posted by nhluhr
and here is the page from the manual that talks about the EGT probe itself:

Can't argue with that!

well... you could... But you'd lose.

-Pete
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Old 11-04-2002, 09:59 PM   #6
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Thanks, Nick! I was just trying to figure out if there was anything relating to this probe slowly dying that would explain why I was seeing 1-2psi LESS boost for the past few months....maybe the damaged probe was always sensing high EGT's? ...just trying to piece things together here...maybe 2 months or so after putting in the uppipe i noticed boost wasn't as high as it was when the pipe first went in.... thanks for the info from the manual by the way!

ron
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Old 11-04-2002, 10:01 PM   #7
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...my car was limpin alright.....a half hour trip around the block and died just about every time i put my foot on the pedal....i'd say more like it was on it's last leg...
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Old 11-04-2002, 10:24 PM   #8
recursian
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Default what are ALL the functions of the OEM EGT sensor??

Where can you get the engine related factory service manual without all of the other manuals? How much does it cost?

Thanks
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Old 11-04-2002, 11:05 PM   #9
zaxrex
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Default Re: what are ALL the functions of the OEM EGT sensor??

something like this?
service manuals
Quote:
Originally posted by recursian
Where can you get the engine related factory service manual without all of the other manuals? How much does it cost?

Thanks
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Old 11-05-2002, 11:45 AM   #10
wrx-spd2
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Default Re: what are ALL the functions of the OEM EGT sensor??

Quote:
Originally posted by ron_c1
ok...i think this is a pretty good question... my EGT sensor just failed, rendering my car something thats looks nice in the driveway but nothing more over the weekend.... i know that the sensor is there basically to let the ECU know if the temp is getting close to a level that could melt the cat in the uppipe.... what else will this trigger? i noticed quite awhile ago that peak boost was down 1-2 psi, and thought it may have been a leak....no leaks were found though. ....could that have been a sign that the sensor was on its way out?? ....just a thought i had....because once i did the 2.2kohm resister....boost was back up to where it was a few months ago... so, is boost limited based on values read from that sensor??
Nick,

I have a PDE up-pipe installed and just got a CEL light... had autozone check it out for me and it was a P0546 code... High EGT... question can I do the 2.2kohm fix on this?... if so did you disconnect the factory egt and plug the 2.2 kohm into the factory socket?...( only a two wire socket)... thx for the help
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Old 11-05-2002, 11:54 AM   #11
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i believe 0546 means you are getting low egt readings.....did you check to see if it's loose yet? ...but yeah...you've got the right idea for the resistor mod....
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Old 11-05-2002, 11:54 AM   #12
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Default Re: Re: what are ALL the functions of the OEM EGT sensor??

Quote:
Originally posted by wrx-spd2


Nick,

I have a PDE up-pipe installed and just got a CEL light... had autozone check it out for me and it was a P0546 code... High EGT... question can I do the 2.2kohm fix on this?... if so did you disconnect the factory egt and plug the 2.2 kohm into the factory socket?...( only a two wire socket)... thx for the help
well it's important to note that the 546 code is for "High voltage input" from that sensor. As you recall from whatever physics class you ever took, resistance in a material rises with temperature so a high voltage from the sensor means the resistance is lower than it should be and it is thusly colder, not hotter (because you don't have a hot cat radiating heat at it).

You can indeed totally eliminate the P0546 and even the P1312 (if you get that one) by doing the 2.2kohm resister mod.

as far as doing the mod, I actually soldered the resistor to the wiring harness for an old broken EGT probe that somebody gave me so I just plugged that in. I've heard that you can merely stick the leads of the resistor into the socket though and that works fine too.
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Old 11-05-2002, 02:53 PM   #13
Fat Ugly Soccer Mom
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dude the same thing just happened to me, and i thought my MAF was bad or something. did you do fix this yet? how hard was it to get to the sensor?
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Old 11-05-2002, 03:11 PM   #14
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Quote:
Originally posted by Fat Ugly Soccer Mom
dude the same thing just happened to me, and i thought my MAF was bad or something. did you do fix this yet? how hard was it to get to the sensor?
It's pretty easy to do....just pop the plastic cover on the passenger side of the engine bay....then trace the wire from the uppipe to that area....unplug it....and plug the leads of the resistor into the connector....i've also been told that your car will run fine with the sensor disconnected without the resistor....but you will have a CEL trigger the low egt temp...
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Old 11-06-2002, 03:10 AM   #15
wrx-spd2
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THX... did the 2.2 kohm fix it took me 5 min. but I'll check to see if I have a loose connection in the up-pipe... I need to replace the gasket... it has a leak... could be the cause of the code???.
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